diff --git a/app/Http/Controllers/Gallery/DefaultController.php b/app/Http/Controllers/Gallery/DefaultController.php
index bfb90da..00ec2f9 100644
--- a/app/Http/Controllers/Gallery/DefaultController.php
+++ b/app/Http/Controllers/Gallery/DefaultController.php
@@ -111,7 +111,7 @@ class DefaultController extends Controller
 
         if (strlen($lastModifiedDate) > 0)
         {
-            $lastModElement = $document->createElement('lastmod', $lastModifiedDate);
+            $lastModElement = $document->createElement('lastmod', date('Y-m-d\TH:i:s+00:00', strtotime($lastModifiedDate)));
             $urlElement->appendChild($lastModElement);
         }